[Docs] Clarify `span_not` query behavior for non-overlapping matches (#27150)

Closes #27134

docs/reference/query-dsl/span-not-query.asciidoc

@@ -1,7 +1,9 @@
 [[query-dsl-span-not-query]]
 === Span Not Query
 
-Removes matches which overlap with another span query. The span not
+Removes matches which overlap with another span query or which are
+within x tokens before (controlled by the parameter `pre`) or y tokens
+after (controled by the parameter `post`) another SpanQuery. The span not
 query maps to Lucene `SpanNotQuery`. Here is an example:
 
 [source,js]
@@ -39,7 +41,7 @@ In the above example all documents with the term hoya are filtered except the on
 Other top level options:
 
 [horizontal]
-`pre`::     If set the amount of tokens before the include span can't have overlap with the exclude span.
-`post`::    If set the amount of tokens after the include span can't have overlap with the exclude span.
+`pre`::     If set the amount of tokens before the include span can't have overlap with the exclude span. Defaults to 0.
+`post`::    If set the amount of tokens after the include span can't have overlap with the exclude span. Defaults to 0.
 `dist`::    If set the amount of tokens from within the include span can't have overlap with the exclude span. Equivalent
             of setting both `pre` and `post`.